Method of treating sodium chloride tails



' .um chloride aus. y

Patented Feb. 1, 1944 lUNITED STATES lPA'IAEN'' GFFICE 2,340,523 l METHOD or' Tammo soDlUM onnonma 'rms Lockwood W. Ferris,Salt Lake City Utah, assignor to Bonneville Limited, New York, N. Y., a

corporation of Delaware Application December 27, 1941, Serial No. 424,571

4 Claims.

This invention relates to improvements in the separation of potasium chloride from sodium chloride by ilotation. The invention provides improvements in such separation which substan- Ltially reduce losses of the valuable potassium chloride yand reduce the cost of recovering it. f'

My copending application Serial No. 376,583, iiled January 30, 1941, vdescribed a 'method of treating crude salt mixtures of potassium and sodium chlorides involving notation of potassium vchloride and the production of sodium chloride tails in a notation treatment and this application sheet, a method embodying the invention but the is a continuation-in-part of my said copending application. l

In the ilotation of potassium chloride from sodium chloride, Withseparation of solid sodium the brine. The solid sodium chloride so obtained contains an appreciable amount of potassium chloride, which, inthe practice of the invention, is recovered. The salt is pulped with sufdcient watcr to form a pulp ofthe proper consistency for pumping, land is pumped to a settling or tails pond in which thesolidsalt is separated from the brine. This brine is saturated with-sodium chloride, but, as considerably more waterv is required to form a. pumpable pulp than is required to dissolve all of the potassium-chloride, it is unsaturated with respect to potassium chloride. 'I'he brine is recycled to pulp a. second batch of tails for pumping to the settling pond, and this circulation of the brine is continued until it is saturated with both sodium and potassium chlorides. The saturated brine is then introduced into an evaporating pond and evaporated to separate out a mixture of potassium chloride andeodium chloride, which, being. substantially identical with the initial feed to the notation apparatus, is supplied with feed to the notation -appartaus Such operation permits substantial economy in the separation of the two salts, because of the recoveryv of the substantial amount of potassium chloride heretofore lost in the sodi- The single figure of the accompanying drawing illustrates diagrammatically `by means of a flow invention is'not limited thereto. The ilow sheet shows the sequence of operations in a conventional manner, the matter illustrated in broken lines being from'the iiow sheet of my said copending application reproduced'here for convenience .to villustrate a complete system in which sodium chloride tails rich in sodium chloride and poor in potassium .chloride may be treated for maximum recovery lof potassium chloride.

In carrying out a method of the invention, sodium chloride tails containing solid particles of sodium chloride, admixed with or adhering to 'potassium chloride, areV treated with fresh water and circulating brine to dissolve all of the potssium chloride and form a brine saturated in respect to both sodium. chloride and potassium' chloride, In treating screened sodium chloride tails, water is mixed with the tails to vform a pulp of the required consistency for pumping. If freshv water is used, it is necessary to use much more water than is required to dissolve the potassium chloride. Such water, accordingly, does not be- The come saturated with potassium chloride. resulting solution saturated with sodium chloride and unsaturated with potassium chloride'is 'circulated in a cyclic manner to repulp successive batches of tails until vthe solution is saturated with respect to both sodium chloride and potas-` sium chloride. Thesaturated solution is separated from the remaining solid sodium chloride and is evaporated to recover a solid product containing the dissolved sodium chloride and potastion, a potassium chloride concentrate is pro-4 duced as a froth.` Briefly. the more general and important features or suchfa method are as fol lows: 'I'he crude salt mixture enters the ball mill where it is mixed with a sumcient amount .of brine saturated in respect to the component salts, to produce a pulp containing, for example, approximately sixty-live percent solids. The salts are preferably ground to separate part of the sodium chloride and potassium chloride parti- 'cles without overgrinding, .and a considerable portion of the salts are insumciently ground.A The ground salts are suitably separated into undersize and oversize portions as by screening.` for ex-A Aample, on an 8-mesh screen, the oversize being.'-

retumed -to the ball mill and the imdersize ad'- mixed `with brine being passed to a pulp box w ere suilicient additional brine is added to i'orm a pulp containing. for example, approximately forty percent -(40%) solids. 'I'his pulp is subjected to notation with the addition oi collector and frother Y reagents which promote theqselective flotation oi one or the chlorides, particularly potassium 6h10- ride. The resulting tails from the notation vcells are o! varying sizes, rich in sodium chloride and poor in potassium chloride andare screened on a suitable screen, for example, one of about 30- mesh, the oversize being returned to the ball mill and the undersize together with the brine being sent to a thickener and then iiltered,

IIn an operation oi' the type illustrated in the flow sheet, the nltered tails are mixed with a sumcient amount oi water to form a pulp which the pump can handle easily. This amount oi.' water will dissolve all of the potassium chloride, but

there is insuiilcient potassium chloride present to make the resultant brine saturated in respect to potassium chloride. It does, however, become saturated in respect to sodium chloride. After the undissolved `salt together withresultant brine has been pumped to the tails pond, the undissolved salt settles outand the free brine drains away from the salt. This brine is saturated in respect-to sodium chloride an perhaps plus or minus one-ilith saturated in r spect to potassium chloride.

This brine is returned for the further repulping o! the salt from the tails illter. Since the brine is not saturated in respect to potassium chloride, it dissolves an additional residual portion ot poleft in the mill tails as a brine saturated in respect to both sodium and potassium chlorides.

This brine is then evaporated to produce a lcrude salt.which will run about thirty percent (30%) potassium chloride and about seventy percent (70%) sodium chloride. I'he crude salts are then run throughl the notation apparatus along with the fresh feed.

Iclaim:

1. In a method of separating potassium chloride and sodium chloride from crude salt mix-v tures( the improvement which comprises grinding ina saturated salt solution the crude salt mixtassium chloride and sodium chloride particles to minimize pulverization' leaving a considerable portion of the crude salt insumciently ground, screening the ground mixture through a coarse screen oi' about 8 mesh to remove the large Dmicles which 'are returned to the grinding operation, subjecting the particleswhich pass through the screen to ailotation treatment to produce a potassium chloride-rich froth and4 a tails rich in sodium chloride but containing considerable potassium chloride, screening the tails and return-` ing the particles on the screen tol the grinding operation, subjecting the particles of the tails which pass through the screento repeated washings with the same` water until' the potassium chloride is dissolved and the water becomes saturated with sodium chloride and contains a considerable amount 'oi potassium chloride. separating the saturated solution from the remaining solid sodium chloride, evaporating the saturated solution to recover the dissolved sodium chloride and potassium chloride and returning the recovered mixture of sodium chloride and potassium chloride to the process.` f 2. In a method of separating potassium chlorid and sodium chloride from crude salt mixtures, ther improvement which comprises grinding in aV saturated salt solution the crudesalt mixture only sumciently to separate in part the potassium chloride and sodium chloride particles to minimize pulverization leaving a. considerable portion of the crude salt insuillciently ground, screening the ground mixture through a coarse screen-voi about 8 mesh to remove the large particles which are returned to the grinding operation, subjecting` I the particles which pass through the screento a flotation treatment to produce a potassium chloride-rich froth and a tails rich in sodium chloride but containing considerable potassium chloride, screening the tails and returning the particles on the screen to the grinding operation,

mixing the particles oi the tails which pass through the screen in a pulping operation with water in an amount suiiicientto forma pulp which `may bev pumped readily, Dumping the pulped tails in`to a receptacle where the water drains 01T the solids, circulating the water from the receptacle over the tails `until, the water is saturated in respect to both potassium chloride and sodium chloride, separating the saturated solution from the remaining solid sodium chloride, evaporating the saturated solution and recovering a solid mixed salt having a similar composition to the original crude salt mixture, and returning the recovered salt to the grinding operation.

3. In a method of separating potassium chloride and sodium chloride from crude salt mixtures, the improvement which comprises grinding in a saturated salt solution the crude salt mixture only l sufficiently to separate in part the potassium turel only suiiiciently to separate `in part the pochloride and sodium chloride particles'to minimize pulverization leaving a considerable portion .of the crude salt insumciently ground, screening the groundfmixture through a coarse screen o1' about 8 mesh to remove the large particles which are returned to the grinding operation, subjecting the particles which pass through/ the screen toa flotation treatment to produce a potassium chloride-rich froth anda tails rich in sodium chloride but containing considerable potassium chloride,

screening the tails on a 30 to 60 mesh screen and returning the particles retained on the screen to the grinding operation, mixing the particles oi the' tails which pass through the screen with fresh water in amount sumcient to form a pulp that can vvbe pumped readily, said water being in an anount in excess of that which may be saturated with,

potassium chloride in the said mixing, separating a solution saturated with sodium chloride and unsaturatedwith potassium chloride from the remaining osolid sodium chloride,v subjecting another portion of tails to mixing with said solution from the mst-mentioned mixing, repeating the mixing ot the said solution with succeeding portions of screened tails until a solution is obtained which is saturated in respect to Sodium chloride andvalmost saturated with potassium chloride, evaporating the'solution oi' potassium assenza chloride and' sodium chloride so obtain s sonoiroduct containing potassium' chlorideand sodium chloride, and returning the solid product to the orocess. l l

4. In amethod of separating potassium-chloride .nd sodium chloride from crude salt mixtures, the improvement which comprises grinding in a satuiated salt solution the crudeI salt mixture only sufficiently toseparate in part the potassium chloride and sodium chloride particles to minimize pulverization leaving a considerable portion of the crude salt insumeiently ground. screening the ground mixture through 'a coarse screen of about 8 mesh to remove the large particles which are returned to the grinding operation. subjecting the particles which pass through the screen to a notation treatment to produce a potassium chloride-rich froth and a tails richin sodium chloride but containing considerable potassium chloride, screening the tails through a 30 to 60 mesh screen and returning the retained particles on the screen to the grinding operation, subjecting the particles `which pass through the screen to repeated washings with the samewater until the potassium chloride is dissolved. said solution becoming saturated with'sodium chloride and from almost completely saturated to completely saturated withv potassium chloride, and evaporating the solution to recover the potassium chloride and the sodium 

